Selective reduction of polynitro aromatics



Patented Feb. 16, 1954 SELECTIVE REDUCTION OF POLYNITRO AROMATICS EdmundW. Lowe, Lafayette,

Ind., assignor to Purdue Research Foundation, Lafayette, 11111.,

a corporation of Indiana No Drawing. Application April 19, 1950, SerialNo. 156,929

16 Claims. (01. 260-580) 1 This invention relates principally to thereduction of polynitro aromatic compounds. More particularly, thisinvention relates to the selective reduction of certain polyintroaromatic compounds, at least one but not all of the nitro groups presentbeing completely reduced to an amino group while at least one nitrogroup remains unaiiected.

The selective reduction of aromatic dinitro com pounds to formnitroamines has long been known in the art. Such reductions are almostinvariably conducted in strongly alkaline solutions and reducing agentssuch as the hydrosulfides, sulfides and polysulfides of sodium arecommonly employed. During the course of the reaction, the sulfide ion ofthe selected reducing agent is oxidized to thiosulfate. By such methodsm-dinitrobenzene has been reduced to m-nitroaniline, 2,6-dinitrotolueneto Z-amino G-nitrotoluene, 2,4-dinitrotoluene to Z-nitro 4-aminotoluene,2,4- dinitroanilin to 1,2-diamino l-nitrobenzene, 2,4-dinitrodiphenylamine to 2 amino 4-nitrodiphenylamine, and the like.

Similar methods have been applied to the selective reduction of varioustrinitro aromatics with varying success. Thus, picric acid (in the formof the sodium salt) is reduced to picramic acid(4,6-dinitro-2-aminophenol) by sodium sulfide, the yield being 75%.However, the application of this and similar reducing methods to 2,4,6-tr'initrotoluene (TNT), certain derivatives of TNT and the like resultin yields of reduction products ranging from zero to poor.

I have discovered an improved method for the selective reduction ofcertain trinitro aromatic compounds whereby thecorrespondingdinitroamino and/or diaminonitro compounds are obtained inyields higher than hitherto believed possible.

One object of my invention is to provide an improved process for theselective reduction of certain trinitro aromatic compounds.

Another object of my invention is to provide an improved process for thereduction of certain trinitro aromatic compounds to the correspondingdinitroamino and/or diaminonitro compounds.

An additional object of my invention is to provide an improved processfor the selectiv reduction of 2,4,6-trinitrotoluene.

A further object of my invention is to provide an improved process forthe reduction of 2,4,6- trinitrotoluene to 2,6 dinitro 4-aminotolueneand/or 2,4-diamino G-nitrotoluene.

Another object of my invention is to provide an 2 improved process forthe selective reduction of condensation derivatives of2,4,6-trinitrotoluene.

Additional objects of my invention will become apparent as thedescription thereof proceeds.

In accordance with my improved process, the sodium hydroculfide, sodiumsulfide, sodium polysulfide, etcetera, reducing agents of the prior artare employed bu the reaction proceeds through a difierent mechanism. Ashas been mentioned previously, in prior art reduction processes withthese reducing agents, the sulfide ion of the selected reducing agent isoxidized to thiosulfate. In my improved process, the sulfide ion ofthese reducing agents is oxidized to free sulfur.

This new reaction mechanism is achieved by conducting my improvedprocess under conditions differing radically from those employed in theprior art. By the practice of my invention, the selective reduction ofcertain trinitro aromatics proceeds with the production of the desiredreduction products in high yields in sharp contrast to the processes ofthe prior art which result in zero yields or, at best, poor yields ofthe reduction products when applied to the same starting materials.

For the better understanding of my invention, it will be explained indetail in the following example in connection with the reduction of TNTto 2,6-dim'tro 4-aminoto1uene (hereinafter referred to as DNAT) and to2,4-diamino 6-nitrotoluene (hereinafter referred to as DANI). It shouldbe emphasized that the following example is illustrative only and iscapable of wide variations with respect to both starting materials andoperating conditions.

E'wample 1 Two gram moles of TNT are dissolved in 1000 cc. ethyl acetateand to the resulting solution is added a strong aqueous solutioncontaining two gram moles ammonium acetate to act as a buffer insubsequent operation. Obviously, if desired, the buffer salt may beformed in situ by adding the appropriate amounts of acetic acid (e. g.,g. glacial acetic acid) and ammonium hydroxide (e. g., cc. of 28-29%ammonia solution) to the ethyl acetate solution of TNT.

The above reaction mixture is vigorously stirred and to it is added,portionwise, over the course of 25-35 minutes, a solution made bydissolving 720 g. of 70% sodium hydrosulfide (9 moles) in 1200 cc.water.

During the reduction reaction, the hydroxyl ion concentration of thereaction mixture would ordinarily tend to increase rapidly in accordancewith the reaction:

I have discovered it is absolutely essential that that increase inalkalinity be prevented and, in fact, that the whole reduction occur atan alkalinity distinctly lower than employed in the processes of theprior art. To this end, a strong acid is added as required and asdescribed in detail subsequently, to maintain the alkalinity of thereaction mixture at the desired level. As a result of extensiveexperimentation, I have determined that the pH of the reaction mixtureshould be maintained the approximate range 7.5 to 8.0 (as determined byHydrion test paper) during the first additions of reducing solution, forexample, during the addition of the first two thirds or thereabouts ofthe reducing solution and in the approximate range of 8.0 to 8.5thereafter.

Most conveniently, the desired alkalinity is maintained by theportionwise addition of a strong acid, for example, hydrochloric acid,as required, said portionwise additions being interspersed as necessarybetween the additions of successive portions of the reducing agent. Inthe present example, a total of about 400 cc. of B. hydrochloric acid isrequired to maintain the reaction mixture at the proper alkalinity leveland this is added preferably in ten or twelve approximately equalportions as conditions require.

As will be evident to those skilled in the art, the presence of ammoniumacetate in the reaction mixture aids materially in maintaining the pHwithin the required range. This buffer salt is highly ionized with theformation of cations and anions which unite respectively with hydroxylor hydrogen ions to form acids or bases that are weakly ionized.Accordingly, during the reduction reaction, as highly ionized sodiumhydroxide forms in accordance with the equation previously given, theresulting hydroxyl ions unite, in large measure, with the ammonium ionsfrom the buffer salt to form the weakly ionized ammonium hydroxide.Thus, due to the presence of the buffer salt, the alkalinity of thereaction mixture increases comparatively slowly. On the other hand, onadding a portion of strong acid to the reaction mixture, the hydrogenions so introduced unite, in large measure, with the acetate ions fromthe buffer salt to form the weakly ionized acetic acid. As a result, theaddition of a portion of strong acid which would, under ordinarycircumstances,

throw the reaction mixture far on the acid side, has, in the presence ofthe buffer salt, relatively little efiect on the pH of the mixture.

While the above explanation has been based on the use of ammoniumacetate as the buffer salt, any ammonium salt will be of benefit in thecontrol of pH as will be salts of weak acids. Salts formed by the unionof a weak base and a weak acid are especially useful. For convenience inoperation, the buffer salt selected should preferably not form insolublehydrolytic products on reaction with water and of course should notreact with the materials employed in the synthesis.

It is obvious that the pH of the reaction mixture can be maintainedWithin the desired range without the use of buffers if an extremelylarge number of very small additions of reducing agent are made, thesebeing interspersed with an extremely large number of very smalladditions of 4 acid. Such operations are tedious and difiicult toconduct on the laboratory scale but in commercial operations, wherelarge volumes are involved, the alternate and frequent additions ofsmall portions of reducing agent and acid to the reaction mixtureimposes no special problems and can be easily accomplishedautomatically, for example, by the use of suitable proportioning pumps.

On adding the initial portion of the reducing agent to the TNT solution,the temperature rises rapidly. Below 50 C., the reaction proceedsslowly, reduction does not proceed to the extent desired and accordinglylow yields of the products sought are obtained. On the other hand, at 70C. or above, low yields are likewise obtained due to the formation oflarge amounts of tar, traces of which also contaminate the desiredreduction compounds resulting in the production of lowered yields ofdark colored products. Accordingly, the spontaneous temperature rise isallowed to proceed until a temperature in the neighborhood of 60 C. isreached following which the temperature is maintained at this level plusor minus 5 C.) by the application of appropriate cooling means asrequired. After some two thirds of the reducing agent has been added,further cooling is unnecessary and should be discontinued. After all thereducing agent has been added, the temperature will gradually increaseto about 70 C. and should be maintained at from 70 C. to the boilingpoint of the solution (about 73 C.) for a period of one hour followingthe last addition of reducing agent, heat being applied to the reactionmixture as necessary and stirring being continued.

After reduction is complete, ethyl acetate is removed by distillation.Due to the presence of large quantities of separated solids in thereaction mixture, it is preferable to agitate during the distillationoperation, the reaction mixture being thinned if desired by addition ofup to say an equal volume of water to facilitate proper stirring.

When removal of organic solvent is complete, the distillation residue iscooled to about room temperature and filtered, the resultingreddishbrown filter cake being washed with three or four times itsvolume of water, the filtrate and washings being discarded.

The washed filter cake is slurried into 2000 cc. of 10% hydrochloricacid and the whole is brought to a boil and filtered hot through apreheated filter. The insoluble material is again extracted by beingboiled with a second 2000 cc. portion of 10% hydrochloric acid followedby filtration as before. The combined filtrates are cooled to roomtemperature and the separated DNAT hydrochloride is removed byfiltration. The DNAT hydrochloride is slurried with three times itsvolume of water which results in hydrolysis of the hydrochloride withseparation of the free base which is filtered, washed thoroughly withwater and dried. Yellowish brown crystals, M. P. 1'71-1'71.5 C.

The dilute hydrochloric acid extracts from which the initial crop ofDNAT has been removed are brought to pH 3 to 5 by addition ofconcentrated ammonia solution. A second crop of DNAT separates as thefree base which is removed by filtration and thoroughly washed withwater and dried. Amorphous yellow solid, M. P. above 0., usuallyl68-1'70 C. Total yield (both crops), 45-50% of theory.

The filtrate from which DNAT has been removed is treated with additionalamounts of ammonia solution until the pI-I is 8. An orange redprecipitate of DANT forms. The slurry is cooled to 20 C. or below withstirring and the DANT separated by filtration and washed with water. TheDANT is frequently contaminated with a small amount of fiocculent greeninsoluble matter. This is easily separated by slurrying the mixture inwater, allowing the comparatively massive DANT crystals to settle anddecanting the still suspended impurity. The deep orange red DANT meltsat 131-133" 0.; yield, 35-40%. On recrystallization from water, themelting point is increased to 134.0-1345" C.

DNAT is tasteless, odorless and burns rapidly with a bright yellow smokyflame. The material is insoluble in petroleum ether, practicallyinsoluble in water, fairly soluble in alcohol, chloroform and benzeneand very soluble in ethyl acetate and dioxane. This amine is soluble tothe extent of 47 g. per liter in glacial acetic acid at 25 C. and 9.1 g.per liter in 10% sulfuric acid at the same temperature. Ten percenthydrochloric acid dissolves 47 g. per liter DNAT at 100 C. and 17 g. perliter at 40 C.

DANT melts in a flame without burning but on further heating ignites andburns with a luminous smoky flame. In the cold, the base is insoluble inheptane, slightl soluble in benzene and ethylene dichloride, fairlysoluble in ethanol and very soluble in ethyl acetate. One liter of waterdissolves about 8 g. at 20 C- DANT forms a monohydrochloride and adihydrochloride; the former can be recrystallized unchanged from waterbut the dihydrochloride is partially converted to the monohydrochlorideby this procedure. The dihydrochloride is very soluble in watercontaining a small amount of hydrochloric acid.

By proceeding in accordance with Example 1, the total amine yield isabout 80-85% of theory and DNAT and DANT are produced in approximatelyequal quantities although slightly more of the monoamine forms. Theratio in which the two. compounds are formed can be varied extensivelyby changing the reducing agent-TNT ratio. As would be expected,increasing the proportion of the reducing agent enhances the productionof the diamino compound. It has also been observed that when very low orvery high ratios are employed to produce predominantly DNAT or DANTrespectively, the total yield of reduction products is somewhat lowerthan when an intermediate ratio is used and the two amines formed inapproximately equal amounts. All these facts can be deduced from thedata presented in the table (Examples 26).

NOTE.The ratio employed in Example 5 is the same as that of Example 1.

To attain the objects of my invention it is essentia1 that the polynitrocompound be highly dispersed or, preferably, partially or completelydissolved in the reaction medium. This is con..-

veniently accomplished through use of a solvent for the polynitrocompound as set forth in Example 1. A large number of solvents aresuitable for the purpose. The use or ethyl acetate has already beendescribed. Ethanol is also suitable although recovery thereof afterreaction requires a more accurate fractionation column than is necessarywith ethyl acetate. Dioxane is reasonably satisfactory as a solvent butits use apparently promotes tar formation, especially if the reductionis-conducted at a slightly higher temperature than recommended.

While by the process of my invention, TNT can be reduced with theformation or DNAT and/or DANT in high yields, as has been mentionedpreviously, the sulfide reduction of TNT by classical procedures givesrise to no amines or, at best, very poor yields of amines. This is shownin Examples 7 to 11, wherein TNT was reduced with a variety of sulfidereducing agents in accordance with classical procedures.

Example 7 TNT, dissolved in a mixture of ethanol and ethyl acetate, wastreated with an aqueous solution of sodium hydrosulfide. The pH of thereaction mixture was not controlled. On working up the reaction product,only a trace of acid soluble material was obtained. Acidification of thereaction liquor gave rise to brown nitrogen dioxide fumes indicatingthat degradation of nitro groups had occurred with formation of nitriteions.

Example 8 A solution of TNT in alcohol or ethyl acetate was treated withan aqueous solution of sodium sulfide at 65 C. At the conclusion of thereaction, 40% of the TNT charge was recovered unchanged together with47% by weight of a high melting, acid insoluble material of unknownstructure. No DNAT or DANT could be isolated and the reaction liquorproduced brown fumes on acidification.

Example 9 Attempts to reduce TNT in organic solution by addition of anaqueous solution of sodium disulfide were unsuccessful. No acid solublereaction products were produced.

Example 10 rise to brown nitrogen dioxide fumes.

Example 11 Hydrogen sulfide was passed through a solution of two molesTNT in 1000 cc. dioxane containing 12 drops concentrated (28-29%)ammonia solution, the temperature being kept below 40 C. After the rateof absorption of the gas had become low, the above quantity of ammoniasolution was again added following which hydrogen sulfide was passedthrough the reaction mixture as before. The sulfur formed was removed byfiltration and, after evaporation of the solvent, a yield of an orangecolored crude was obtained of which less than 50% was soluble in boiling10% hydrochloric acid. A yield of DNAT of about 25% was obtained fromthe acid soluble material. On repeating the reaction at 50 60 0., theDNAT formed was contaminated with a black tar which could amine.

not be separated from the,

As the foregoing examples show, by the practice of my invention, TNT canbe reduced with the formation of DNAT and/or DANT in high yields and therelative proportion of the two amines in the product can be varied atwill over a wide range. On the other hand, the reduction of TNT inaccordance with the various procedures of the prior art for thereduction of TNT or similar polynitro aromatic compounds usually resultsin the formation of no acid soluble product of any kind. In a fewinstances, prior art procedures result in the formation of aminereduction products but the yield is invariably low, only DNAT is formedand frequently this is contaminated with tars so as to render the amineunsuitable for use as a starting material for further synthesis.

While my invention has been described largely in connection with theselective partial reduction of TNT, it may be applied to a large varietyof polynitro aromatic compounds among which may be mentioned symmetricaltrinitrobenzene, 2,4,6- trinitrobenzoic acid, 2,4,6-trinitrophenylethylalcohol, materials formed by the condensation of2,4,S-trinitrophenylethyl alcohol with secondary amines such asdiethanol amine, morpholine, etcetera, 2,4,6 trinitrostilbene, 2,4,6trinitrostyrene, 2(2,4=,6'-trinitrophenyl) furan and the like. Theprocess of my invention can also be applied to the selective reductionof dinitro aromatics such as m-dinitrobenzene, 2,6-dinitrotoluene,2,4-dinitrotoluene, 2,4-dinitroaniline, 2,4- dinitrodiphenylamine andthe like but fair to excellent methods for the selective reduction ofthese compounds are described in the prior art.

The amines produced in accordance with my invention are widely useful,for example, as intermediates in the preparation of sulfur colors and ofazo colors of the pigment type, the insoluble dye type and the solubledye type. DNAT,

for example, has great utility as the diazotizable component in themanufacture of azo colors. Due to the presence of two nitro groups onthe ring, each in meta position to the amino group, colors made byreacting diazotized DNAT with a suitable coupling component are usuallystronger I and deeper in shade than those obtained from diazotizedp-toluidine or diazotized mononitro p-toluidines. Furthermore, pigmenttype or insoluble dye type azo colors made by reacting diazotized DNATwith a suitable coupling component are usually less soluble in oils andlacquer solvents than the corresponding colors obtained with diazotizedp-toluidine or diazotized mononitro p-toluidines.

DANT is useful either as the diazotizable' or tetrazotiaable componentor as the coupling component in the preparation of azo colors. Thus,DANT may be tetrazotized and coupled with two molecular equivalents of asingle coupling component or, usually successively, with one molecularequivalent of each of two coupling. components. When a single couplingcomponent is employed, both coupling reactions may occur at the sameposition on the coupling component or, with some coupling components, itis possible to so control reaction conditions that the two couplingsproceed separately and successively and occur at different positions onthe coupling component. Azo colors produced by reactin tetrazotized DANTwith appropriate coupling agents are usually stronger and deeper inshade than the corresponding colors produced from tetrazotizedm-phenylene diamine or tetrazotized 2,4-toluylene diamine. Also, thecolors from tetrazotized DANT, if of the pigment or insoluble dye.type,

8 are usually less soluble in oils and lacquer solvents thancorresponding colors obtained from the other diamines just mentioned.These benefical effects are attributed to a nitro group in DANT meta toboth amino groups.

DANT is also an excellent coupling component, giving azo colors usuallysurpassing the corresponding colors obtained when using m-phenylenediamine or 2,4-toluylene diamine as the coupling component in strength,shade and (with pigment type or insoluble dye type colors) insolubilityin oils and lacquer solvents. Obviously, DANT may be used both as thediazotizable or tetrazotizable component and the coupling component informing an azo color. Thus, tetrazotized DANT may be coupled with onemolecular equivalent of DANT following (or preceding) which thetetrazotized DANT is coupled with a molecular equivalent of a secondcoupling component. Or, if desired, the tetrazotized DANT may be coupledwith two molecular equivalents of DANT, this obviously resulting in acolor analogous in structure to Bismark brown.

DNAT and DANT, especially the latter, are of utility in producing sulfurcolors of the immedial yellow type. Thus, DANT may be fused with sulfurto produce an orange yellow color. If desired, this color may beproduced by fusing the crude reaction mixture (after removal of organicsolvent and filtration but prior to extraction of amines therefrom)produced by reducing TNT with about six molecular equivalents of asulfide reducing agent in accordance with the teachings of thisinvention (see Example 6).

Be it remembered, that while my invention has been described inconnection with various specific details thereof, these are illustrativeonly and in no way limit the scope of my invention except as these maybe included in the accompanying claims.

I claim:

1. A process for the selective reduction of polynitro monocyclicaromatic compounds carrying not more than three nitro groups on thebenzene nucleus comprising adding an alkali metal sulfide to a solutionof such a polynitro aromatic compound and removing alkali produced bysaid reduction at the rate necessary to maintain the reaction mixturealkaline and belorv approximately pH 8.5.

2. A process for the selective reduction of polynitro monocyclicaromatic compounds carrying not more than three nitro groups on thebenzene nucleus comprising adding an alkali metal sulfide to a solutionof such a polynitro aromatic compound in the presence of an ammoniumsalt of a weak acid and removing alkali produced by said reduction atthe rate necessary to maintain the reaction mixture alkaline and belowapproximately pH 8.5.

3. A process for the selective reduction of polynitro monocyclicaromatic compounds carrying not more than three nitro groups on thebenzene nucleus comprising the portionwise addition of an alkali metalsulfide to a solution of such a polynitro aromatic compound whilemaintaining the reaction mixture alkaline and below approximately pH 8.5by additions of a strong acid thereto interspersedly with respect tosaid additions of reducing agent.

4. A process for the selective reduction of polynitro monocyclicaromatic compounds carrying not more than three nitro groups on thebenzene nucleus comprising the portionwise addition. of an alkali metalsulfide to a solution of' such a polynitro aromatic compound in thepresence of an ammonium salt of a weak acid while maintaining thereaction mixture alkaline and below approximately pI-I 8.5 by additionsof a strong acid thereto interspersedly with respect to said additionsof reducing agent.

5. A process for the selective reduction of 2,4,6-trinitrotoluenecomprising adding an alkaline metal sulfide to a solution of2,4,6-trinitrotoluene and removing alkali produced by said reduction atthe rate necessary to maintain the reaction mixture alkaline and belowapproximately pH 8.5.

6. A process for the selective reduction of 2,4,6-trinitrotoluenecomprising adding an alkali metal sulfide to a solution of2,4,6-trinitrotoluene in the presence of an ammonium salt of a weak acidand removing alkali produced by said reduction at the rate necessary tomaintain the reaction mixture alkaline and below approximately pH 8.5.

'7. A process for the selective reduction of 2,4,6-trinitrotoluenecomprising the portionwise addition of an alkali metal sulfide to asolution of 2,4,6-trinitrotoluene while maintaining the reaction mixturealkaline and below approximately pH 8.5 by addition of a strong acidthereto interspersedly with respect to said additions of reducing agent.

8. A process for the selective reduction of 2,4,6-trinitrotoluenecomprising the portionwise addition of an alkali metal sulfide to asolution of 2,4,6-trinitrotoluene in the presence of an ammonium salt ofa Weak acid while maintaining the reaction mixture alkaline and belowapproximately pH 8.5 by additions of a strong acid theretointerspersedly with respect to said additions of reducing agent.

9. A process for the preparation of 2,6-dinitro 4-amino toluenecomprising adding approximately three molecular equivalents of an alkalimetal sulfide to a solution of 2,4,6-trinitrotoluene and removing alkaliproduced by said reduction at the rate necessary to maintain thereaction mixture alkaline and below approximately pH 8.5.

10. A process for the preparation of 2,6-dinitro 4-amino toluenecomprising adding approximately three molecular equivalents of an alkalimetal sulfide to a solution of 2,4,6-trinitrotoluene in the presence ofan ammonium salt of a weak acid and removing alkali produced by saidreduction at the rate necessary to maintain the reaction mixturealkaline and below approximately pH 8.5.

11. A process for the preparation of 2,6-dinitro 4-amino toluenecomprising the portionwise addition of approximately three molecularequivalents of an alkali metal sulfide to a solution of2,4,6-trinitrotoluene while maintaining the reaction mixture alkalineand below approxi mately pH 8.5 by additions of a strong acid theretointerspersedly with respect to said additions of reducing agent.

12. A process for the preparation of 2,6-dinitro e-amino toluenecomprising the portionwise addition of approximately three molecularequivalents of an alkali metal sulfide to a solution of2,4,6-trinitrotoluene in the presence of an ammonium salt of a weak acidwhile maintaining the reaction mixture alkaline and below approximatelypH 8.5 by additions of a strong acid thereto interspersedly with respectto said additions of reducing agent.

13. A process for the preparation of 2,4-diamino B-nitrotoluenecomprising adding approximately six molecular equivalents of an alkalimetal sulfide to a solution of 2,4,6-trinitroluene and removing alkaliproduced by said reduction at the rate necessary to maintain thereaction mixture alkaline and below approximately pH 8.5.

14. A process for the preparation of 2,4-diamino S-nitrotoluenecomprising adding approximately six molecular equivalents of an alkalimetal sulfide to a solution of 2,4,6-trinitrotoluene in the presence ofan ammonium salt of a weak acid and removing alkali produced by saidreduction at the rate necessary to maintain the reaction mixturealkaline and below approximately pH 8.5.

15. A process for the preparation of 2,4-diamino 6-nitrotoluenecomprising the portionwise addition of approximately six molecularequivalents of an alkali metal sulfide to a solution of2,4,6-trinitrotoluene while maintaining the reaction mixture alkalineand below approximately pH 8.5 by addition of a strong acid theretointerspersedly with respect to said addition of reducing agent.

16. A process for the preparation of 2,4-diamino G-nitrotoluenecomprising the portionwise addition of approximately six molecularequivalents of an alkali metal sulfide to a solution of2,4,6-trinitrotoluene in the presence of an ammonium salt of a weak acidwhile maintaining the reaction mixture alkaline and below approximatelypH 8.5 by additions of a strong acid thereto interspersedly with respectto said additions of reducing agent.

EDMUND W. LOWE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,878,950 Lyford Sept. 20, 1932 2,464,194 Zimmerman Mar. 8,1949 OTHER REFERENCES Tiemann, Berichte, vol. 3, p, 217 (1870).

1. A PROCESS FOR THE SELECTIVE REDUCTION OF POLYNITRO MONOCYCLICAROMATIC COMPOUNDS CARRYING NOT MORE THAN THREE NITRO GROUPS ON THEBENZENE NUCLEUS COMPRISING ADDING AN ALKALI METAL SULFIDE TO A SOLUTIONOF SUCH A POLYNITRO AROMATIC COMPOUND AND REMOVING ALKALI PRODUCED BYSAID REDUCTION AT THE RATE NECESSARY TO MAINTAIN THE REACTION MIXTUREALKALINE AND BELOW APPROXIMATELY PH 8.5.